Horrifying new details of how three members of a family attending a Christmas party were killed by a poisoned cake have been revealed for the first time.

Zeli Silva Dos Anjos, 61, who baked the traditional Brazilian festive treat, was among seven people who attended a pre Christmas annual party on December 23 - but only four survived.

Now MailOnline can reveal that there were two cakes baked for the party - and the family could have been spared if they had chosen to cut the second, safe cake instead of the one that turned out to be poisoned with arsenic.

Other revelations, revealed by a member of the tragic family who spoke for the first time included how:

The family believe the killer cake could have been poisoned by an outsider who had a deadly grudge The poison took effect so quickly that guests began writhing in agony within minutes of tasting the cake Mrs Anjos is now ‘horrified by guilt’ as she remains in critical condition in hospital - and the family fear for her recovery Previously unconfirmed suggestions that a member of the wider family had died last year from eating poisoned bananas are true

The disturbing new details were revealed by close relative Isabel Moraes who described in detail for the first time the circumstances surrounding the tragedy at Torres near Porto Alegre in southern Brazil as she spoke to MailOnline this morning.

Ms Moraes told how, within hours of tucking in, her sister in law Maida Bernice Flores da Silva, 58, Neuza Denize Silva Dos Anjos, 65, and Neuza’s daughter Tatiana Silvia Dos Santos, 43, were all dead - and authorities later revealed traces of deadly arsenic were found in their bodies.

Zeli and her 10-year-old great nephew Mateus, Tatiana’s son, were also taken ill and rushed to hospital.

Speaking exclusively to MailOnline, Maida’s sister-in-law Isabel said: 'Zeli is horrified by what’s happened. She is overcome with guilt because it was her cake that caused the tragedy, but we keep telling her not to worry and that it was an accident.

‘We said she shouldn’t blame herself, but she is getting so anxious it’s not doing her recovery any good. She is getting worse instead of getting better. She is on a ventilator to help her breathe and we don’t know when she will be discharged.’

Revealing for the first time the sequence of events leading up to the tragedy, Isabel, 54, a psychologist, said: 'Every year Zeli baked the cake and every year everyone meets up for a family get together to celebrate Christmas and be with each other, we are all extremely close.

'That day two cakes were made. One by Zeli and one by Maida, but it was only Zeli’s which was eaten. If they had eaten the other one then perhaps this wouldn’t have happened.

'Both were on the table and Jefferson said it was decided to leave Maida’s cake and have Zeli’s because she was the one who made it every year but as soon as they started to eat it, they felt ill.

'Jefferson told me that within a few minutes they were all saying it had a bitter sour taste and by this time Zeli had eaten two slices but as soon as everyone started to complain she said ‘Stop, no one eat any more.’

However, a short while later everyone who had eaten the cake was doubled up in agony vomiting and ambulances raced to Maida and Jefferson’s apartment in Torres to take the group to hospital.

The only guest not to suffer any ill effects was Neuza’s husband Joao who doesn’t eat cake, while Jefferson was discharged by doctors after a few hours.

Maida was the first to die on Christmas Eve, while Neuza lost her life a few hours later and her daughter Tatiana was the last to pass away with their funeral services held on Christmas Day and Boxing Day.

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‘We have a cousin who is a chemist, and he said that there is no way such a large amount of arsenic could have been produced by out-of-date ingredients, so it makes us wonder if someone tampered with it.’

Isabel added: 'It’s strange that just our family is involved though. Even the policeman said he’d never seen a case like this.

‘You have to wonder if it is something deliberate from someone, but it won’t be Zeli. I think if this is a deliberate action, it will be someone with a grudge against the family, but I have no idea who that could be - or what their motive is.’

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Isabel also confirmed what other relatives had told MailOnline, that Zeli’s husband Paulo died in September from food poisoning after eating bananas suspected to have been contaminated by chemicals following the flood.

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She said: 'Zeli told me what happened at Paulo’s funeral a few months ago. They work up as usual and Paulo went to make coffee while she mashed up some bananas for their breakfast.

'They ate them with a little bread and drank the coffee and then went for a walk but after a few minutes he said he didn’t feel well and then started to vomit and a few minutes later she started to vomit as well.

‘A neighbour saw them being sick and called an ambulance and they went to hospital. Zeli recovered quickly but Paulo just got worse and eventually died. We all said at the time the bananas must have been contaminated by the flood waters.’